Atmospheric Corrosion Behavior of Aluminized Steel Sheets.

Abstract

Aluminized steel sheets are promising materials for use as maintenance-free roofing or siding because of their superior corrosion resistance in comparison to galvanized steel sheets in a corrosive atmospheric environment. In this paper, the corrosion behavior of aluminized steel sheets has been investigated using test panels exposed for over 30 years. Corrosion of aluminized steel sheets was slight and their surfaces were covered with corrosion products mainly containing Fe.

Corrosion Behavior of Aluminized Steel Sheets in 50-Year Outdoor Exposure Test

“…Magnetite was also detected in the corroded regions of the steel substrate inside the alloyed layer, and in the corroded regions of the aluminized layer and the corrosion product build-up regions of the aluminized layer surface. As described in the previous report 4) regarding the aluminized steel specimens exposed for 31 years, it is known that when Fe corrosion products are formed, the presence of Al ions facilitates the formation of goethite. The detection of goethite in the corroded regions of the steel substrate inside the alloyed layer (where many Al ions are apparently supplied) agrees with the results of the report.…”

“…It was reported that a corrosion depth of 50 μm was recognized in the steel substrate of Type 1 specimens after 31 years of exposure. 4) The corrosion depth increased to 0.1 mm in the Type 1 specimens exposed for 50 years. Corrosion of the steel substrate mainly occurred near the cut edges.…”

“…Figure 5 shows cross-sectional optical micrographs of typical corroded regions in Types 1 and 2. As indicated by the investigation results of the specimens exposed for 31 years (Type 1) in the referenced report, 4) the corrosion of the aluminized layer reached the alloyed layer and the corrosion factors reached the steel substrate through cracks in the alloyed layer. The steel substrate consequently corroded and the resultant corrosion products built up and expanded to ultimately push up the alloyed layer locally.…”

“…Type 2 appeared whiter than Type 1. From the investigation results of the specimens exposed for 31 years, 4) this appearance change is estimated to have occurred because the steel substrate partly corroded and the resultant corrosion products covered the specimens' surface.…”

“…The detection of goethite in the corroded regions of the steel substrate inside the alloyed layer (where many Al ions are apparently supplied) agrees with the results of the report. 4) On the other hand, magnetite is increasingly formed toward the surface layer, where fewer Al ions are supplied. Goethite is known as stable rust on weathering steels, and may also contribute to the corrosion resistance of aluminized steel sheets.…”